The present invention relates to the improvement of the load capability and rigidity of a linear guide assembly which receives loads through a number of balls which circulate, while rolling, in ball rolling passages extending through the guide rail and the slider slidable on the guide rail.
An example of this type of the linear guide assembly is disclosed in a Japanese Utility Model Examined Publication No. Hei. 6-646. In the disclosed linear guide assembly, at least three rows of ball rolling grooves, or upper, medium and lower ball rolling grooves, are formed in each side of a guide rail. A slider, which is slidable on the guide rail, has legs extending along both sides of the guide rail. Each of the legs of the slider includes ball rolling grooves respectively disposed in opposition to the ball rolling grooves of the guide rail, and ball circulating passages parallel to the ball rolling grooves thereof. A number of balls are put in the ball circulating passages. With movement of the slider, the balls circulate through the ball circulating passages while rolling therein. As shown in FIGS. 1(a) and 1(b), each of balls B contacts, at two points (T1 and T2), with the surface of a ball rolling groove of a guide rail 1 and the surface of a ball rolling groove of a slider 2, which is disposed so as to face the corresponding ball rolling groove of the guide rail 1. Prolonged lines L1 to L3 each connecting the contact points T1 and T2 are converged at intersection points O1 and O2, located inside the guide rail 1.
Another conventional linear guide assembly of the same type is disclosed in a Japanese Utility Model Unexamined Publication No. Sho. 64-53622. As shown in FIGS. 2(a) and 2(b), the linear guide assembly has also a three-row ball rolling groove structure. In the passages defined by the upper and lower ball rolling grooves of the slider and the guide rail, which are confronted with each other, each ball contacts, at two points T1 and T2, with the surfaces of its associated ball rolling grooves being confronted with each other. In the passage defined by the medium ball rolling grooves facing each other, each ball contacts, at four points T1 to T4, with the surfaces of the ball rolling grooves of the guide rail and the slider.
When the intersection points (converging points) of the prolonged lines connecting the contact points of the balls with the groove surfaces are located inside the guide rail, an elastic displacement of the linear guide assembly is increased against a moment load acting on the slider so as to roll the slider, and the linear guide assembly exhibits an self-aligning function. On the other hand, when the converging points are located outside the guide rail, the linear guide assembly exhibits a high rigidity against the moment load.
In the Japanese Utility Model Examiner Publication No. Hei. 6-646 shown in FIGS. 1(a) and 1(b), its load capacity is limited to a load capacity corresponding to only two rows of ball rolling grooves. The reason for this is that when a load F acts on the upper side of the slider 2 (FIG. 1(a)) or a load f acts on the lower side thereof (FIG. 1(b)), the load is received by one or two rows of ball rolling grooves.
The load capacity of the Japanese Utility Model Unexamined Publication No. Sho. 64-53622, as shown in FIG. 2(a), is limited to that corresponding to two rows of the ball rolling grooves as of the Japanese Utility Model Examiner Publication No. Hei. 6-646 shown in FIGS. 1(a) and 1(b). The linear guide assembly may be constructed such that the load is received by the upper, medium and lower ball rolling grooves, as shown in FIG. 2(b). In this case, the intersection points O1 and O2 of the prolonged lines L1 to L3 connecting the contact points T1 to T4 are located separately inside and outside the guide rail 1, and the self-aligning function fails to operate and the rigidity against the moment load is low. In this respect, this is impractical.
Further, in an actual use of the linear guide assembly, the upward and downward loads acting on the linear guide assembly are generally different in their magnitudes. To increase the rigidity of the linear guide assembly against an excessively load acting thereon, a measure may be taken in which an increased pressure is merely applied in advance to the linear guide assembly may be made. However, the measure results in an excessive increase of the prepressure, possibly leading to the damage of the linear guide assembly.
In the Japanese Utility Model Unexamined Publication No. Sho. 64-53622, there is no description on a ratio of the radius of curvature of the flank of the groove of the ball rolling passage to the diameter of the ball (the ratio will be referred to as a groove R ratio), although the linear guide assembly of the publication is unique in that the ball contacts at four points with the groove surfaces in the medium ball rolling passage, and the ball contacts at two points with the groove surfaces in the upper and lower ball rolling passages. Incidently, in the conventional linear guide assembly, referred to above, which has two rows of ball rolling passages, the groove R ratios of the two rows of ball rolling passages are equal. The conventional linear guide assembly having three rows of ball rolling passages has not yet been put into practice. In designing this linear guide assembly for its actual use, the structure of the linear guide assembly having two rows of ball rolling passages will be directly applied to the linear guide assembly.
The load capacity and rigidity of the linear guide assembly become large with increase of the contact area of the ball and the ball rolling passage. To increase the load capacity and rigidity at a fixed ball size, it is only needed to reduce the radius of curvature of the flank of the ball rolling passage.
FIG. 3 is a diagram showing the relationship between the groove R ratios and contact angles of the flanks of the ball rolling grooves, which define the ball rolling passages in which each ball contacts with the groove surfaces at two points. In the ball rolling passage shown in FIG. 3(a), the flank f of the ball rolling groove Ma has the radius of curvature R1. In the ball rolling passage shown in FIG. 3(b), the flank f of the ball rolling groove Mb has the radius of curvature R2. Here, R1 greater than R2. Since the radius of curvature is small (a groove R ratio of the radius of curvature of the flank f to the diameter of the ball 210 is small), a contact area Sb, elliptical in shape, of the ball rolling groove Mb where it contacts with the ball 210 may be larger than a contact area Sa, elliptical in shape, of the ball rolling groove Ma (Sb greater than Sa). If the contact area is large, the load capacity and rigidity of the linear guide assembly are increased. The reason why the contact area is elliptical is that the ball rolling grooves Ma and Mb are linear in the direction vertical to the paper of the drawing.
The relationship between the groove R ratios (the radii of curvature) and contact angles of the flanks of the ball rolling grooves, which define the ball rolling passage in which each ball contacts with the groove surfaces at four points, will be described with reference to FIG. 4. In FIG. 4, for ease of explanation, the curvature radii R1 and R2 of the right and left flanks fL and fR of a Gothic arch groove Mg are different from each other; R1 (left) greater than R2 (right). Let an initial contact angle xcex8 be 45xc2x0 for both the flanks fL and fR (flanks indicated by one-dot chain lines). In this case, the center of the curvature of the left flank fL is O1, and that of the right flank fR is O2.
The curvature centers O1 and O2 of the flanks fL and fR are displaced to positions O1xe2x80x2 and O2xe2x80x2, respectively. For a change quantity xcex1 of the contact angle xcex8 of the ball 210, a change quantity xcex11 of the contact angle of the ball on the right flank having the curvature radius R2 is much greater than a change quantity xcex12 of the contact angle on the left flank having the curvature radius R1, although the displacement quantities (offset values) A1 and A2 of the curvature centers are equal to each other.
Thus, in the ball rolling passage having four contact points, contact conditions of the ball and the ball rolling grooves are easy to change, so that basic characteristics of the linear guide assembly, such as load capacity, rigidity and rolling frictional force, also change.
Where the radius of curvature of the ball rolling groove of the ball rolling passage having four contact points is small, a small error of the contact angle of the ball on the ball rolling groove greatly affects the function and characteristics of the linear guide assembly. For this reason, the accuracy control in working the product is difficult. Where four contact points are used and the radius of curvature is small, the contact area is large and the slide is great. Where the radius of curvature of the ball rolling groove of the ball rolling passage having four contact points is large, the load capacity and the rigidity of the resultant linear guide assembly are in unsatisfactory levels. Thus, a designer encounters an antinomic problem in designing the linear guide assembly.
Accordingly, an object of a first aspect of the present invention is to solve the above-mentioned problem of the conventional liner guide assembly, particularly to provide a linear guide assembly having the following advantages: When the slider receives a load (F) acting on the upper side thereof as to press it against the guide rail or a load (f) acting on the lower side thereof as to move it apart from the guide rail, the upper, medium and lower ball rolling grooves receive the load in share. When a moment acts at a right angle to the lengthwise direction of the guide rail, the linear guide assembly exhibits a high rigidity against the moment load When a mounting error is created in assembling the linear guide assembly, the linear guide assembly exercises the self-aligning function to absorb the error, if it is within a tolerable range.
To achieve the above object, there is provided a linear guide assembly according to the first aspect of the present invention, in which a slider is mounted on a guide rail having three rows of ball rolling grooves on each side thereof, three rows of ball circulating passages are formed in each of two legs of the slider which extend above and along both the sides of the slider, a number of balls being put in the ball circulating passages, each of the ball circulating passage including a ball rolling groove disposed facing the corresponding ball rolling groove of the guide rail, the opposed ball rolling grooves forming a first ball rolling passage, a ball return or second passage parallel to the ball rolling passage, and curved passages, one of the curved passages interconnecting the first ends of the first and second ball rolling passages, while the other interconnecting the second ends of the first and second ball rolling passages,
wherein
1) in the upper or lower load ball rolling passage, each ball contacts, at four points, with the surfaces of the ball rolling grooves of the guide rail and the slider, while in the remaining two ball rolling passages, each ball contacts, at two points, with the surfaces of the ball rolling grooves of the guide rail and the slider, and
2) intersection points of one of lines each connecting the two opposite contact points of those four contact points of the upper or lower ball rolling passages, and lines connecting respectively the two opposite contact points of the remaining two ball rolling passages are located inside or outside the guide rail.
In the linear guide assembly thus constructed, the prolonged lines, each of which connects the contact points of each ball where the ball contacts with the surfaces of the ball rolling grooves therein, are oriented in the same directions. Therefore, all loads acting on the slider are received in share by three rows of ball trains within the three upper, medium and lower ball rolling passages. Therefore, the linear guide assembly exhibits its maximum load capacity against the load.
The prolonged lines, each of which connects the contact points of each ball where the ball contacts with the groove surfaces, converge at points located inside or outside the guide rail. Therefore, when the linear guide assembly receives a turning effect (moment load) in the direction orthogonal to the lengthwise direction of the guide rail, the linear guide assembly exhibits a high rigidity or an self-aligning function.
For the above background reasons, a second aspect of the present invention is made and has an object to provide a linear guide assembly having three rows of ball rolling passages which is capable of satisfying the requirements of high load capacity and high rigidity, and selecting such a load capacity as not to increase a ball rolling resistance in accordance with the direction of the load applied to the sliding block by such a unique technical idea that two or three rows of ball rolling passages receive a load acting on the assembly, and the number of the rows of ball rolling passages used is selected in accordance with the direction of the load applied.
To achieve the above object, there is provided a linear guide assembly according to the second aspect of the present invention, in which a sliding block is mounted on a guide rail having three rows of ball rolling grooves on each side thereof, three rows of ball circulating passages are formed in each of two legs of the sliding block which extend above and along both the sides of the sliding block, a number of balls being put in the ball circulating passages, each of the ball circulating passage including a ball rolling groove disposed facing the corresponding ball rolling groove of the guide rail, the opposed ball rolling grooves forming a first ball rolling passage, a ball return or second passage parallel to the ball rolling passage, and curved passages, one of the curved passages interconnecting the first ends of the first and second ball rolling passages, while the other interconnecting the second ends of the first and second ball rolling passages,
in which in at least two ball circulating passages, each the ball contacts, at four points, with the surfaces of the ball rolling grooves of the guide rail and the sliding block.
In the linear guide assembly thus constructed, in all the ball circulating passages, each ball contacts, at four points, with the surfaces of the ball rolling grooves. Therefore, the linear guide assembly receives a load applied to the sliding block through the balls on the ball rolling grooves of the ball circulating passages. Therefore, the linear guide assembly exhibits its maximum load capacity and high rigidity to the load applied thereto, independently of the direction of the load.
In at least two ball circulating passages, each ball contacts, at four points, with the surfaces of the ball rolling grooves, whereby the linear guide assembly exhibits its maximum load capacity and high rigidity against the load acting thereon in every direction. The remaining ball circulating passage is arranged such that each ball therein contacts at two points with the surfaces of the ball rolling grooves, in consideration with the direction of the load acting on the sliding block. The linear guide assembly thus constructed receives the load by at least two rows of balls. In a direction where the load is large, the linear guide assembly receives the load by three rows of balls. Therefore, the load capacity and rigidity of the linear guide assembly may be selected to be as large as possible so long as the rolling resistance is not increased.
In addition, an object of a third aspect of the present invention is to provide a linear guide assembly which are improved in its load capacity and rigidity without reducing the radius of curvature of the ball rolling grooves contacting with the ball at four contact points, or while keeping easy accuracy control, and without little increasing rolling friction of balls. The present invention is based on the following facts:
1) The load capacity and rigidity are increased where the radius of curvature of the two-contact-point groove is smaller than that of the four-contact-point groove.
2) The two-contact-point groove is originally low in rolling friction. Therefore, even if the radius of curvature of the groove is reduced, an increase of the rolling friction is not great.
To achieve the above object, a linear guide assembly according to the third aspect of the present invention in which a sliding block is mounted on a guide rail having three rows of ball rolling grooves on each side thereof, three rows of ball circulating passages are formed in each of two legs of the sliding block which extend above and along both the sides of the sliding block, a number of balls being put in the ball circulating passages, each of the ball circulating passage including a ball rolling groove disposed facing the corresponding ball rolling groove of the guide rail, the opposed ball rolling grooves forming a first ball rolling passage, a ball return or second passage parallel to the ball rolling passage, and curved passages, one of the curved passages interconnecting the first ends of the first and second ball rolling passages, while the other interconnecting the second ends of the first and second ball rolling passages,
wherein
1) of three rows of the first ball rolling passages, at least one row of the first ball rolling passage is arranged such that each ball contacts, at four points, with the groove surfaces, while the remaining rows of the first ball rolling passages are arranged such that each ball contacts, at two points, with the groove surfaces,
2) a groove R ratio of the flanks of the ball rolling grooves of each of the first ball rolling passages where each ball contacts at two points with the groove surfaces, is more than 50% but smaller than that of the flanks of the ball rolling grooves of the first ball rolling passage where each ball contacts at four points with the groove surfaces.
The above mentioned construction may be modified such that a groove R ratio of the flanks of the ball rolling grooves of each of the first ball rolling passages where each ball contacts at two points with the groove surfaces, is more than 50% but less than 53%, and a groove R ratio of the flanks of the ball rolling grooves of the first ball rolling passage where each ball contacts at four points with the groove surfaces, is between 53% and 56%.
In the construction according to the third aspect of the present invention, of the three rows of ball rolling passages formed on each side of the linear guide assembly, only one row of ball rolling passage is arranged such that each ball contacts, at four contact points, with the groove surfaces. The remaining two ball rolling passages are arranged such that each ball contacts, at two points, with the groove surfaces. In the ball rolling passages of the two contact points, the rolling friction of the ball is low, and even if the radius of curvature of the groove is small, the rolling friction of the ball is increased not so much. A groove R ratio of the groove of each of those ball rolling passages of the two contact points is set to be smaller than of the ball rolling passage of the four contact points. Thus, the radius of curvature of the groove of the four-contact-point ball rolling passage remains as intact, but the radius of curvature of the groove of each two-contact-point ball rolling passage, the working of which is relatively easy and its working little affects the rolling friction, is reduced. As a result, the load capacity and rigidity are increased with a little increasing of the rolling friction. The groove R ratio of each two-contact-point ball rolling passage is set at more than 50%. The reason for this is that at 50% of the groove R ratio, the size (radius) of the ball is equal to that of the ball rolling groove, and the entire range of the flank when viewed in the radial direction comes in contact with the ball, to thereby provide a maximum contact area.
In the modification of the above-mentioned construction according to the third aspect of the present invention, the groove R ratio of each two-contact-point ball rolling passage is set to be more than 50% but less than 53%. The reason for this is that if the groove R ratio is not more than 50%, the radius of curvature of the groove is below the radius of the ball, viz., such a groove is nonsense, and if it exceeds 53%, it is impossible to secure the required load capacity and rigidity.
As for the four-contact-point ball rolling passage, if its groove R ratio is less than 53%, the contact area is excessively large, the rolling friction is noticeable, and the working of grooves and its accuracy control are difficult. If the groove R ratio exceeds 56%, it is impossible to secure the load capacity and rigidity in excess of those of the conventional four-contact-point ball rolling passage.
In the linear guide assembly of the invention, the groove R ratio of the ball rolling groove of the four-contact-point ball rolling passage is used as intact, viz., it is set at a value approximately equal to that of the ball rolling groove of the two-contact-point ball rolling passage, so as not to make it difficult to work the grooves and to control the accuracy in the working of the grooves. The groove R ratio of the ball rolling groove of the two-contact-point ball rolling passage, in which the rolling friction of the ball is originally low, is set at a value smaller than of the conventional one. Therefore, the load capacity and rigidity can successfully be increased while keeping easy working of grooves and easy control of working accuracy and little increasing the rolling friction of the balls.